1. Field of the Invention
The present invention relates to a polyurethane foam and a method of manufacturing the same, and in particular relates to a polyurethane foam used in washing implements, cosmetic puffs, filters, sealing materials, cushioning materials, damper materials and sound-absorbing materials, and a method of manufacturing the same.
2. Description of the Related Art
From hitherto, polyurethane foams have been widely used in washing implements, cushioning materials, industrial materials and so on. Such polyurethane foams are obtained by foaming the reaction product between a polyisocyanate and a polymer polyol. As such polyurethane foams, polyether type polyurethane foams in which a polyether polyol is used as the polymer polyol, and polyester type polyurethane foams in which a polyester polyol is used as the polymer polyol are known. Of these, polyether type polyurethane foams are relatively inexpensive, and are used in many ways.
However, such polyurethane foams are hydrolyzable. Hydrolyzability is a phenomenon in which macromolecules are decomposed by water; hydrolysis is accelerated under high-temperature high-humidity conditions, and results in a drop in strength, discoloration, a drop in volume and so on, and in severe cases disintegration. Due to hydrolysis, according to environmental tests as described later, the retention rate of the tensile strength and the elongation between before and after the test is 65% or less, and in severe cases the foam breaks easily and cannot even be handled
Moreover, such polyurethane foams may be degraded by heat or ultraviolet radiation. As a result, such degradation occurs during use outside or under a high-humidity environment, and hence such use is not possible. Moreover, there is a problem known as ‘gas yellowing’ in which discoloration to a yellow color occurs during use through gases such as NOx. Moreover, there is a problem in that the heat resistance as represented by the compression set is not sufficient, and with packing and so on, in the case of being compressed for a long period at high temperature, the compressive stress drops, and recovery does not readily occur.
There are thus calls for polyurethane foams that are excellent in terms of hydrolysis resistance, light resistance, yellowing resistance and heat resistance, and have high strength.